'Zoe's law' would reclassify a foetus of more than 20 weeks as a 'person'. Photograph: Vincenzo Lombardo/Getty Images

A final meeting between a coalition of women's groups and a NSW MP, to try to amend a bill the groups believe could lead to abortion becoming illegal, has ended in a stalemate.

The NSW parliament is due to debate "Zoe's law", which will class a foetus as a living person in particular circumstances, on Thursday.

Women's lobby groups vehemently oppose the bill and met the MP introducing it, Chris Spence, on Tuesday morning to try to thrash out a compromise.

The chief executive of Family Planning NSW, Ann Brassil, who was at the meeting, said the groups wanted the wording which would make the a foetus a living person taken out.

"We are not looking at any further discussions about that amendment to the bill. At this point we just want the bill defeated," she told Guardian Australia. "From Chris Spence's perspective, the words living person embodied the essence of the bill."

The potential law was named after Brodie Donegan's unborn baby Zoe, who was stillborn after Donegan was hit by a car when she went for a walk on Christmas Day while eight months pregnant in 2009.

Donegan, who is pro-choice, wanted charges of manslaughter or murder laid against the drug-affected driver of the car but because Zoe technically died in her mother's womb she was listed as part of Donegan's injuries and the driver was charged with grievous bodily harm.

Spence is Donegan's local MP and the pair have worked on the bill together and worded it so that anything done to the foetus with the mother's consent - including abortion - would not be punishable under the potential new law.

Groups opposed to the bill, including the NSW Bar Association, believe it could have unintended consequences such as setting a legal precedent that would lead to abortion becoming illegal.

"Our legal advice was that there wasn't an alternative set of words to those of living person that would protect women in the way we require, so we informed Chris of this and we agreed given his unwillingness on the form of words around living person, we agreed to differ and we will now continue our lobbying against the bill," Brassil said.

"It was an amicable meeting."

The bill was due to be debated last Thursday but, at the urging of the coalition of women's groups, Spence delayed it for a week to allow them time to meet him and other MPs.

Brassil believes opposition to the bill is growing within the parliament but stopped short of saying she believed it would be defeated.

"Because it's a conscience vote, we are talking to individuals, rather than the party rooms themselves and my view would be there is increasing concern around the bill as they are getting more information about unintended consequences of the bills," she said.

"People are also firming up in their views that this piece of legislation is unnecessary because it doesn't add anything to existing legislation so I'm pleased with how we're progressing with our lobbying but I don't think our job is done yet if we truly want to protect the women. We've got work to do yet."

After the meeting with Spence a range of groups including the NSW bar association, Women's Health NSW, Rape and Domestic Violence services of Australia, the Women's Electoral Lobby, an independent lawyer and women's legal services gave presentations to a cross-section of MPs and their representatives from the NSW parliament.

Brassil would not say her confidence was growing that the bill would be defeated and said there was a range of religious and rightwing organisations and individuals lobbying for the bill to pass.

"This is essentially not an abortion debate. This is about the unintended consequences of legislation that isn't required and some individual groups are saying this is about pro-choice, pro-abortion groups but it's not; this is about the very great concerns about unintended consequences of the bills," she said.